1. Field of the Invention
The present invention relates to a semiconductor wafer surface treatment method and, more particularly, to a method of treating a surface of a semiconductor wafer so that one surface of the wafer may be mechanically damaged for gettering of contaminants.
2. Description of the Related Art
Along the development of micropatterning of semiconductor elements, it becomes important that influence due to various types of contamination in element manufacturing processes is decreased. For example, contamination with heavy metals such as Cu or Fe reduces life time of minority carriers, thus changing characteristics of a transistor, or increasing a leakage current. In addition, by contamination with sodium (Na), mobile ions are generated in an oxide film, thereby degrading stability of an operation of the elements.
So-called gettering is well-known as such a method of cleaning contamination of a semiconductor substrate generated in a manufacturing process. This gettering includes hydrochloric acid oxidation, phosphorus gettering, and the like which are performed during manufacturing processes. In another technique, a silicon wafer serving as a starting material has a gettering ability. In addition, gettering of a substrate includes intrinsic gettering which utilizes oxygen precipitate in the substrate, back side damage (to be referred to as a BSD hereinafter) which causes the back-side surface of the wafer (an opposite side surface to a major surface on which semiconductor elements are formed in the later steps) to be mechanically damaged or distorted, and the like.
Sandblasting is known as a conventional method of forming the above BSD. In this method, a solution obtained by dispersing fine particles of alumina is sprayed to a back-side surface of the silicon wafer to form a mechanical damage. Although this method is effective to form a mechanical damage, the method cannot provide high purity of the silicon wafer required in the manufacture of the semiconductor element. More specifically, the solution obtained by dispersing fine particles of alumina contains very small amounts of metal impurities such as Fe, Cr, Ni, and Cu. Surface analysis using an ion microanalyzer frequently demonstrated that these impurities are strongly attached to and remain on a wafer material as a surface contamination after the treatment. In addition, the back-side surface of the wafer is a roughened surface, and three-dimensional micropatterns are present therein. However, since a solution containing an alumina is sprayed to this uneven surface, the fine particles of alumina fill the recessed patterns in the back-side surface of the wafer. For these reasons, process defects are undesirably caused in manufacturing processes of the semiconductor element, as in the case of surface contamination due to metal impurities.
In a conventional case, treatment processes of the semiconductor wafer are performed in a clean room to manage cleanliness. However, in the sandblasting treatment process, fine particle of alumina solution is sprayed with high pressure. Therefore, the cleanliness in operation environment can be hardly maintained.
As described above, formation of BSD using the conventional sandblasting undesirably has low cleanliness.